PLN'S jLN'D FINGEBS. 125 



throau'h the water, they hai n:vr also to afford support to 

 the animal while creeping up on land. This e nee ted a 

 in j lid oat ion both or the sste_eton ani 01 the muscles ol 

 the limes. The number of dn rays was gradually lessened 

 and was finally reduced to rive. These five remaining 

 ■• however, developed more vigorousiy. The suft 

 cartilaginous rays became hard iones. The rest of the 

 skeleton also became comsii-rally more firm.. The move- 

 ments of the body became not only more vigorous, but 

 also m:re varied. The separate portions of the skelet:n 

 system, ani cense opaentiy those of the muscular system also. 

 -: ■■...: more ani m:re iizerentiated. Owing :: the intimate 

 katiou of the noaasoular to the nervous system the latter 

 als: - .y male markei pr: gross in point of function 



md strototare, We therefore rhui thot the crain is very 

 much more devel:ped in the higher Ampkiiia than in 

 Fishes, in lMui-hh.es. aui in the lovrer Amphibia.. 



The organs which are most modified in consequence ::' 

 an amtohiiious mole of lire are. as we hove already men in 

 the Double-breathers Lie oooo .those :: respiration and 

 of the circulation of the blood. The first advance in 

 organization necessitated by the transition from aquatic to 

 terrestrial habits of life was. of course, tioe formation of an 

 air-breathing organ., a lang This developed 'directly from 

 die swimming-bladder width these animals hai inherited 



.mm suo :o;huate t: the mice ancient organ, use i for the 

 respiration 01 water, the gills.. Hence we find that the 

 lowest Amphibia, the Gined Amphibia, like the Dipneusta 

 spend the greater pan of their laves in the water, and that 

 accordingly they breathe water through gilds. It is only 



